When excellent electrical property and mechanical property are required as a surface protective film of a semiconductor element, an interlayer insulation film or a stress relaxation layer of multilayer connection in a package, heat-resistant resin films such as a polyimide film, a polyamide film, a polyamideimide film, and a polybenzoxazole film are generally used. In recent years, due to the shift to high integration of semiconductor devices, downsizing of packages, and the surface mounting by means of solder reflow or bump techniques, demands for the adhesiveness between the heat-resistant resin film and a package material, such as an underfill material, a film material, an adhesive, and a sealant, have been more and more sophisticated. In particular, the adhesiveness between a heat-resistant resin film and an epoxy resin compound has been required to the same level as the initial value of the semiconductor device even after exposure to a heat cycle or high temperature and high humidity environments. Since the insufficient adhesiveness lowers product life cycle or yield in production, a plasma treatment of the surface film has been widely conducted using an oxygen gas, a fluorohydrocarbon gas, a mixed gas thereof, or an inert gas such as argon.
Patent Reference 1 discloses a technique for enhancing the adhesiveness between a polyimide film and an anisotropically-conductive film by means of oxygen plasma treatment to the polyimide film. It is disclosed that the oxygen plasma can remove organic contaminations on the surface of the polyimide film, and enhance the bond strength by forming functional groups thereon, but the adhesiveness after exposure to a heat cycle or high temperature and high humidity environments is not discussed. Further, Patent Reference 2 discloses a flexible printed wiring substrate obtained by laminating a copper foil via an adhesive composition on a polyimide film which was plasma-treated at low temperature so as to integrate them. It is disclosed that as a gas type for plasma treatment at low temperature, any of an inert gas, oxygen gas, or carbon monoxide gas can be used, so that the adhesiveness relative to the copper foil can be enhanced. However, similarly to Patent Reference 1, the adhesiveness after exposure to a heat cycle or high temperature and high humidity environments is not discussed, either.
Further, Non-Patent Reference 1 discloses the adhesiveness between a polyimide film plasma-treated with various gases and a metallic film. Unlike the above-mentioned Patent Reference 2, effects are exhibited only when a nitrogen gas is used for copper film, while the adhesiveness under high temperature and high humidity is not conducted. On the other hand, Non-Patent Reference 2 discloses influence of a plasma treatment using various gases on the adhesiveness between polyimide films. Unlike Patent References 1 and 2, however, it is disclosed that oxygen plasma treatment dose not improve both the bond strength at the initial value and the adhesiveness after an acceleration test (PCT: pressure cooker test) under high temperature and high humidity. Further, while the bond strength at the initial value is significantly improved in nitrogen plasma treatment, the bond strength is abruptly lowered after exposure to high temperature and high humidity environments for more than 100 hours. The bond strength both at the initial value and after exposure to the environments for a long period of time is greatly improved only in a plasma treatment using a mixed gas of oxygen+carbon tetrafluoride.
Thus, in the conventional arts for improving the adhesiveness of heat-resistant resin films using a plasma treatment, the effect of plasma treatment is greatly differed depending both on materials to be laminated thereon and on gas types to be used for the plasma treatment. This has not yet given clear guideline for the sophisticated demands for the adhesiveness of heat-resistant resin films required for the recent semiconductor devices. In addition, it is empirically known that, depending on the gas types for the plasma treatment, a deteriorated layer such as a carbonized layer may be formed on the surface of the heat-resistant resin films, resulting in the deterioration of the wet property on the surface of the heat-resistant resin films and lowered operability in production and increased deficiency for products in the next step. Furthermore, the adhesiveness between the heat-resistant resin films and adhesive materials laminated thereon after exposure to high temperature and high humidity environments is not discussed at all. Accordingly, the plasma treatment used in the conventional arts cannot be directly applied to current semiconductor devices with a bump structure mounted.
Patent Reference 1: Japanese Unexamined Patent Publication No. 2003-73862    Patent Reference 2: Japanese Unexamined Patent Publication No. 2003-163451    Non-Patent Reference 1: Polymer Preprint, Japan Vol. 38, No. 11, pp 3708-3710 (1989)    Non-Patent Reference 2: The IEICE (Institute of Electronics, Information and Communication Engineers) Transaction, C-II, Vol. J74-C-II, No. 6, pp 489-497 (1991)